Much effort has been expended toward the development of systems for collecting oil both inshore and offshore. Results from these efforts have not been particularly encouraging. Major problems have been encountered in oil escapement from boom-skimmer arrangements due to the effects of waves as well as currents and due to structural strength and stability difficulties. The various structurally oriented troubles that have confronted investigators conducting sea tests of prototype equipment are actually easier to rectify for they are within the realm of accomplishment. The oil escapement problems caused principally by wind, waves, and currents on the other hand are a severe challenge, because the solution requires a significant advancement in the state of the art of oil spill clean-up technology. Accordingly, the present invention provides several basic departures from other concepts which have been utilized in the development of various equipment for cleaning oil spills.
Tests conducted with prior art skimming vessel devices have shown that oil can escape boom-skimmer arrangements while influenced by the orbital water particle motion associated with modest 3 foot waves in negligible currents and that rigid skimming vessels allow oil to escape because of a lack of conformance of the skimmer with respect to the wave profile. Based on such tests, the skimming system configuration of the present invention was developed with a skimming vessel which is articulated along its length with regard to the sides of the vessel and/or its bottom baffles, thereby providing conformance superior to prior art skimming vessels by moving like a roller coaster over the waves. When presented with oil in a towing tank, the skimmer of this invention, because of its excellent conformance characteristics, collected in excess of 95% of the oil presented at a forward velocity of 1.7 feet per second and a wave height-to-length ratio of 1/9, where by comparison a conventional skimmer would be ineffective.
Secondly, the present invention provides a means for containing oil at a current velocity magnitude twice that for a conventional oil skimmer. Oil can be contained with the device of this invention with less than 5% throughput loss at a velocity of 2 feet per second where conventional concentrating skimmers are limited to a maximum velocity of 1.25 feet per second. The basic principle involved is to slow down the effective current inside the concentration area while at the same time allowing the oil to enter horizontally. In the process of this invention, the oil is retained on or quite near the surface of the water within the confines of the concentrator for skimming. The virtually horizontal path of the oil into the concentrator is important in the instance of heavy weathered oils and emulsions because any forces tending to push the oil downward will result in oil sweeping under and past the skimming vessel prior to re-surfacing.
Thirdly, in order to increase the skimming capacity of skimming systems, the prior art has resorted to the use of oil booms as a means of increasing the effective width of the skimming vessel. Inasmuch as booms will allow oil underflow in currents or under tow unless all portions of the boom are held at an acute angle with the current, the prior art practice has in one case resorted to using a rope or cable harness to restrain boom elements into a "V" shape in front of the skimming vessel rather than allowing the boom to take the natural catenary shape. Difficulties with the harnessed "V" arrangement, which is itself an improvement over the natural catenary used previously, still exist. First, the harness tends to foul or entangle in use, thereby causing the V configuration to "buckle". Secondly, the two forward towing vessels must remain at a proper distance apart so as to retain the boom configuration, a requirement which is difficult to fulfill in appreciable waves and currents. Thirdly, the rope harness near the surface of the water during towing or in currents will tend to emulsify the approaching oil slick, thereby making skimming more difficult. The present invention provides a converging double boom diverter which overcomes these problems.
Accordingly, it has been concluded that the best approach to a skimming system lies in combining the above noted oil concentration concepts which yield high oil-to-water ratios at high current velocities with the articulated skimming vessel concept which allows excellent wave conformance characteristics, as well as providing an effective forward diverting boom device. The present invention therefore overcomes difficulties due to wave conformance inadequacies and low current limitations, thus providing a successful and economical solution to the problems of the prior art, as will be apparent from the following description thereof.